Field of the Invention
The present invention relates generally to saving power in a portable device which includes a measurement engine and, more specifically, to a portable device with a Global Navigational Satellite System (GNSS) receiver that maintains a desired level of accuracy in its GNSS solutions while minimizing resource usage such as power consumption by the GNSS receiver.
Description of the Related Art
Satellite navigational systems provide positional and sometimes time information to earth-bound receivers. Each system has its own constellation of satellites orbiting the Earth, and, in order to calculate its position, a receiver in that system on Earth uses the satellites “in view” (i.e., in the sky above) of that system's constellation. Generally, the larger the number of satellites in view, the more accurate the calculation of the receiver's position will be. “Global Navigational Satellite Systems (GNSS)” is often used as the generic term for such systems, even though such navigational satellite systems include, e.g., regional and augmented systems—i.e., systems that are not truly “global.”
As the electronics for GNSS receivers have gotten smaller, and the positional calculations have become more accurate, the use of GNSS functions has become ubiquitous in consumer and other electronic devices, from cellular telephones to automobiles. And, as the number of uses for GNSS receivers has grown substantially and is still growing, the number of GNSS systems, both planned and presently operational, is also growing. The widely-known, widely-used, and truly global Global Positioning System (GPS) has been joined by one other global system, the GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS), and will be joined by the Galileo and Beidou systems—each of which has, or will have, its own constellation of satellites orbiting the globe.
Regional systems (those that are not global, but intended to cover only a certain region of the globe) include the Quasi-Zenith Satellite System (QZSS) and the Indian Regional Navigational Satellite System (IRNSS) currently being developed. Augmented systems (which are normally regional as well, and which “augment” with, e.g., messages from ground-based stations and/or additional navigational aids) include Wide Area Augmentation System (WAAS), European Geostationary Navigation Overlay Service (EGNOS), Multi-functional Satellite Augmentation System (MSAS), and GPS Aided Geo Augmented Navigation (GAGAN). The term “GNSS,” as used herein, covers any type of navigational satellite system, global or not, unless expressly indicated otherwise.
Multi-constellation GNSS receivers receive signals from more than one satellite constellation (e.g., two or more of GPS, Galileo, GLONASS, and/or Beidou) and provide much greater accuracy because the number of unblocked satellites, sometimes referred to as satellite/space vehicles (SVs), overhead at any time from several constellations is always greater than the number of SVs overhead from a single constellation. The term “GNSS receiver,” as used herein, covers any type of GNSS receiver, global or not, single or multi-constellation, unless expressly indicated otherwise.
FIG. 1 is a simplified, conceptual representation of a portable device 100 with a GNSS receiver. A System Control Engine 110 controls at least the components related to measurement, positioning, and navigation. Among these, there are a GNSS Measurement Engine 121, Measurement Engine 123, Measurement Engine 125, and other possible measurement engines. Measurement Engines 123 and 125 and the other possible measurement engines may be based on a variety of sources, and provide a wide variety of environmental information. Navigation Engine 130 takes in the measurement information and calculates a navigation solution. As would be understood by one of ordinary skill in the art, a number of feedback loops are normally implemented in regards to a navigation engine, which continually adjust and correct various parameters as, e.g., signal conditions change. In that regard, many of the parameters of the GNSS Measurement Engine 121 may be adjusted, such as, e.g., the duty cycle of the GNSS Measurement Engine 121, how many or which satellites to track (in order to generate measurements for a period of time), etc.
However, although GNSS receivers are getting smaller, more accurate, and ubiquitous, a fundamental problem remains: calculating position/time solutions with a GNSS receiver is a resource-intensive operation. In fact, the GNSS components while operating in a cellular telephone can be the single largest user of power—even during a telephone conversation.
Thus, there is a need for a method to reduce the resource-intensive nature of GNSS reception and processing in a portable device, while also maintaining a desired level of positional accuracy.